Heat transfer systems utilizing a refrigerant circulating through an evaporator and a condenser are well known. A heat transfer system wherein the refrigerant self-circulates, i.e. gravity and buoyancy are forces driving the circulation of the refrigerant, is sometimes referred to as a thermosiphon.
Many electronic component housings need to be cooled due to the heat generated by the electronic components inside the housing. A cooling fan directing air through the housing is sufficient for some applications and/or under certain operating conditions. For other applications a heat transfer system utilizing a refrigerant, which evaporates in an evaporator and condenses in a condenser, might be required. In such a system the evaporator is arranged to cool the electronic components by using heat from the electronic components to evaporate the refrigerant.
WO99/60709 discloses a method and an apparatus for cooling electronic components of radio base stations installed at elevated locations. An evaporator of a thermosiphon cooling system is in thermal contact with heat-generating electronic components to be cooled. A condenser of the thermosiphon cooling system is arranged above the evaporator. The condenser is constructed and arranged for natural convection of ambient air.
Generally, a modern radio communication system comprises a radio access network and a number of communication devices. The radio access network is built up of several nodes, in particular, radio base stations. The primary task of a radio base station is to send and receive information to/from the communication devices within a cell served by the radio base station. In many cases, the base station is run 24 hours a day. Therefore, it is of particular interest and importance to ensure that the base station is operable predictably and reliably. The radio base station comprises an electronic component housing. Inside the electronic component housing there are arranged electronic components and circuitry for performing different tasks of the radio base station. For example, the circuitry may comprise a power control unit, a radio unit comprising a radio amplifier, and a filtering unit for performing corresponding tasks.
Heat generated in the circuitry of the base station, in particular the radio unit, may not always dissipate naturally to a sufficiently high degree. Instead, heat is accumulated in the circuitry and the temperature of the circuitry increases. The increased temperature of the circuitry may impair the performance of circuitry within the radio base station. Consequently, unpredicted interruptions in operation of the base station may occur.
This is clearly not desired and a thermosiphon cooling system as disclosed in WO99/60709, mentioned above, could be used to cool the electronic component housing. WO99/60709 does however not disclose how cooling may be controlled in a thermosiphon cooling system. Under certain conditions it is namely desirable to not cool the electronic component housing in order to avoid a too low temperature inside the electronic component housing, which also could harm the electronic components and circuitry inside the electronic component housing.
WO99/30091 discloses a cooling capacity control for a thermosiphon system. The thermosiphon system has a refrigerant circuit, to which there is connected a branch pipe leading to a container. The container is in some situations filled with refrigerant and in other situations it is empty, the refrigerant having been transferred through the branch pipe to the refrigerant circuit. The amount of refrigerant in the container, and thus the cooling capacity of the thermosiphon system, is controlled by means of a heater. When high cooling capacity is required from the thermosiphon system, the container is not heated. Thus the container remains filled with refrigerant. When less cooling capacity is required, the container is heated such that some of the refrigerant boils. Liquid refrigerant is expelled from the container by the gas pressure in the container. The refrigerant circuit is flooded with liquid refrigerant and thereby the cooling capacity of the thermosiphon system is reduced.